The present invention relates to a method of manufacturing a buried heterostructure semiconductor laser and, more particularly, to a method of manufacturing a buried heterostructure semiconductor laser using metalorganic vapor phase epitaxy.
When a buried heterostructure semiconductor laser is to be manufactured, the step of burying a mesa structure including an active region is required. When this step is performed by metalorganic vapor phase epitaxy, since a growth rate of a metalorganic vapor phase epitaxy is controlled by a mass transport mechanism, abnormal growth occurs at both the ends of the mesa structure. For this reason, it is difficult to bury the mesa structure flat.
In a conventional technique, as shown in FIG. 7, a mesa structure having a small height (h&lt;1 .mu.m) is used, and growth of a buried layer is repeated twice to form a buried heterostructure laser element. Alternatively, as shown in FIG. 8, when a mesa structure having a large height is to be used, a selection mask 14 on the upper portion of the mesa structure is formed as an overhang to suppress the growth of both the ends of the mesa structure, and buried layers are grown to form the laser structure. In FIGS. 7 and 8, reference numeral 11a denotes an n-type InP substrate; 11b, an Se-doped n-type InP buffer layer on the substrate 11a; 12, an undoped InGaAsP active layer; 13, a p-type InP cladding layer; and 14, an SiO.sub.2 film for forming a selection mask. In addition, reference numeral 15 denotes a p-type InP current blocking layer; 16, an n-type InP current confining layer; 17, a p-type InP over-cladding layer; and 18, a p-type InGaAsP cap layer.
According to the conventional technique using the mesa structure having a small height shown in FIG. 7, however, a film thickness of 1.2 .mu.m or more is required to sufficiently block a current by a p-n reverse bias of buried layers consisting of the p-type InP current blocking layer 15 and the n-type InP current confining layer 16. As a result, as shown in FIG. 7, the buried layers largely protrude (1.0 .mu.m or more) at both the ends of the mesa structure. When the buried layers protrude at both the ends of the mesa structure, it is difficult that a buried layer is grown by the second growth of a buried layer to flatten the surface of an element, and trouble may occur in the steps of isolating electrodes and elements.
In addition, according to the conventional technique using the selection mask having an overhang, as shown in FIG. 8, the mesa structure must be formed by wet etching, and the controllability of a mesa shape is not good. For this reason, uniformity and controllability of laser characteristics are degraded and the yield of lasers is decreased accordingly.